Vocabulary size is a topic that can lead to all sorts of heated
discussions, hurt feelings, unjustified pride, and never-ending
debates. The reason why this is so is because having a large
vocabulary size is often seen as being an enviable trait, whilst
discovering that one has merely an average vocabulary size, which, by
definition, most people do, leaves many people feeling that they need
to reach for a dictionary and start learning some new words. So what
is it about vocabulary size that makes it so important to measure? Why
bother making an entire website devoted to testing vocabulary
knowledge?

For an international project like this, I’d like to attract as wide an audience as
possible to investigate the course of vocabulary acquisition and
compare that course across different native languages (L1). Certainly
the course would be different for language learners whose L1s are
cognate with the target language (L2) they are studying. And for those
that are not cognate, there are probably differences among them as
well depending on factors such as the degree of similarity between the
two languages’ phonemic inventories,
morphological typologies, and even
writing systems. Even the prevalence of L1
loan words in active use in the target L2 may affect the course of
vocabulary acquisition.

There is a fundamental problem with many, perhaps most, vocabulary
tests which is rarely acknowledged. It's not always clear what the
problem is because intuition tells us that testing knowledge of a word
should be easy and the result should be unambiguous; either one knows
a word or does not. But the reality is much more complicated than
that.